Steel drum industry production and technology development gains and losses talk (2)
Li Jisheng
Since the steel drum products of our factory were used exclusively by the troops, they are mainly used to hold steam and diesel oil, so there is no need for internal coating of anti-corrosion coating. After the army was transferred to the people, with the continuous expansion of the market share of civilian products, the steel drums were increasingly diversified, and the steel drums of our factory began to contain corrosive substances. In order to meet the user's requirements for the corrosion resistance of steel drums, our factory began to develop the internal corrosion protection barrels in 1993. At that time, there were three common methods of corrosion protection in steel drums:
1 lined plastic bag method: This method is mainly used for full-opening barrels to hold solid objects;
2 built-in plastic barrel method: mainly used for full-opening barrels, which can hold liquid and solid substances;
3 Internal spraying method: It can be used for the production of open or closed barrels, which can hold a variety of liquid or solid media.
Among the above three anti-corrosion methods, the internal spraying method has become a commonly used internal anti-corrosion form in the steel drum industry at a low cost, wide applicability, good mechanical strength and impact resistance. In view of this, the focus of our discussion is on how to obtain a high quality internal corrosion resistant coating.
In order to adapt to the production line, we have introduced a rotary cup type electro-spraying line. The production process of the inner spray drum is shown in Figure 1.
After the phosphating treatment, the barrel is transported by the transmission chain after preheating. The spray gun mounted on the trolley is pushed from the outside to the inside at a constant speed. At the same time, the high-speed rotating spray cup mounted on the tip of the gun sprays the powder coating onto the inner wall of the steel drum under the action of an electrostatic high-voltage electric field. The gun automatically returns when it travels to the end of the drum and continues to spray during the return trip. The thickness of the coating can be adjusted by controlling the powder flow valve or the speed of the spray gun trolley.
Figure 1 Schematic diagram of the spray line
In order to ensure the adhesion of the coating and the uniformity of the thickness of the coating, it must be ensured that:
1 The inner wall of the barrel is clean, free of oil and other debris;
2 The gas source for conveying the powder is clean and dry, and the pressure is constant;
3 The work site is clean, dry and dust-free;
4 electrostatic high voltage generator power supply voltage is stable;
5 After the smooth and no bumping state, the sprayed barrel is sent to the next process (drying process).
The spraying process requirements and construction conditions of the top and bottom of the bucket are similar to the above, except that the spray gun can be kept in place without the feed stroke of the gun body.
The drying temperature of the epoxy resin coating is about 130 ° C - 160 ° C, and the drying time is about 10 min - 20 min. Accurate drying time and arch drying temperature are related to steel drum specifications, sheet thickness and coating thickness, and must be explored through practice.
Drying of powder coatings requires more requirements for ovens than electrostatic coatings. Therefore, it is necessary to use hot air curtains, hot air circulation and other means to ensure that the temperature difference between the upper and lower parts of the oven is as uniform as possible (within ±5 °C). If the temperature difference is too large, due to the principle of rising hot air, the upper temperature of the oven will be too yellow or even coked, and the lower part will not solidify due to the low temperature. In order to minimize the occurrence of such defects, compared with the drying method in which the barrel body is longitudinally placed, the drying method using the barrel body horizontally can effectively reduce the height of the oven, thereby effectively reducing the temperature difference between the upper and lower portions of the oven, and coating The drying quality of the layer will be better.
The powder coating method should be equipped with a powder recovery device to reduce the amount of powder splash to ensure the working environment of the workers. The recovered powder can be reused after being treated, which is beneficial to reduce the production cost. In addition, an open flame is prohibited at the work site to ensure safety.
It should be specially stated that for the barrel body and the top of the barrel welded by the automatic welding machine, the inner surface of the whole barrel body can be uniformly and uniformly coated during the internal spraying, and no static spraying dead angle (due to the electrostatic shielding effect); The barrel and the top of the barrel welded by the semi-automatic welding machine have electrostatic spray dead angles, as shown in Figure 2. A coating with a reliable anti-corrosion effect cannot be formed at the corner of the corner, which means that the steel drum does not have the ability to resist corrosion of the corrosive medium to be contained. Therefore, if special measures are not taken (such as using a fully automatic welding machine to weld the barrel or special filling powder at the corner of the barrel top cover) to solve the problem of static dead angle, the anti-corrosion barrel produced by this spraying method has great anti-corrosion ability. The reason is that the phenomenon that the anti-corrosion barrels frequently occur in China every year is corroded.
Figure 2 Schematic diagram of electrostatic shield dead angle
The quality of the coil in the drum closure directly affects the quality of the sealing of the steel drum. The cost of the steel directly affects the cost of the steel drum. Therefore, improving the structure of the coil and adjusting the locking process of the coil and the top of the barrel have great economic benefits for each steel drum factory.
Figures 3 and 4 are schematic views of two types of coils.
Figure 3 Schematic diagram of the closure coil commonly used in China
Figure 4 Schematic diagram of the closure coil using Trisure patented technology
Figure 3 is a schematic diagram of the spiral ring commonly used in China. The production process is as follows:
Blanking Stretching - Shaping Punching - Trimming - Turning Reaming - Tapping.
Figure 4 shows the spiral produced by Tri-sure technology. The production process is:
Blanking Stretching - Shaping Punching - Extrusion Octagon - Leveling - Turning Reaming - Tapping.
We know that the role of the octagonal in the coil structure is only to prevent the rotation of the locked coil from rotating in the upper barrel. Therefore, by analyzing the process of the two, it can be seen that, compared with FIG. 4, the coil of FIG. 4 can effectively satisfy the requirements of the use of the coil, and can save steel (the thickness of the coil is thin and there is no edging and trimming waste). It is really the crystallization of human wisdom.
It is a pity that there are still very few manufacturers using coils of this structure in the steel drum industry in China. I believe that this kind of coil with better economic benefits should be promoted in the steel barrel industry as soon as possible.
Fig. 5 and Fig. 6 are schematic diagrams of two types of screw locking.
Figure 5 Schematic diagram of the type I coil lock structure
Figure 6 Schematic diagram of the type II spiral locking structure
Fig. 7 and Fig. 8 are schematic views showing the deformation of the two kinds of lock type coils after the steel drum falls.
Fig. 7 Schematic diagram of drop deformation of type I spiral locking structure (sealing liner failure, leakage)
Fig. 8 Schematic diagram of drop deformation of type II spiral locking structure (sealing ring does not fail, no leakage occurs)
Figure 5 lock-type seal is guaranteed by a gasket in an appropriate amount of compression. After the drop test, the collar is out of bounds and in a free state, thereby causing the entire lock structure to lose its sealing performance. Figure 6 lock type seal is guaranteed by a gasket in an appropriate amount of compression. After the drop test, the gasket is still in an effective sealed state, thus ensuring that the entire lock area maintains its sealing performance after undergoing large deformation.
From this we can draw the following conclusion: Compared with the lock type of Figure 5, the lock structure of Figure 6 has better anti-drop leakage performance, so this lock type should become the main screw of steel drum manufacturers. Ring lock type. Although this type of lock has certain drawbacks, it can be easily solved according to the method provided in the article "Research on Improving the Reliability of Steel Bar Seals" (see "Steel Barrel" magazine). These two types of locks are used in our factory.
The problem of thinning steel drums has been proposed for many years, and in some cases, manufacturers have been promoted one after another. I believe that this method of fully exploiting the excess function of traditional steel drums has at least the following advantages:
1 can bring good economic benefits to manufacturers;
2 Compared with the thick plate, the pressure deformation of the thin plate is easier, which is beneficial to ensure the quality of the bead of the steel drum.
Therefore, in recent years, our factory has also tried to reduce the thickness of steel drums, and has been applied to some specifications of steel drums, and achieved good economic benefits.
The gains and losses of China's steel barrel industry in the past two or two decades
After 20 years of unremitting efforts of the steel barrel industry colleagues, it can be said that China's steel barrel industry has improved personnel quality, product quality and equipment quality.
The improvement of personnel quality is mainly reflected in:
1 The leaders of the steel barrel industry have broad visions and broad information channels, which can guide the development of the industry and the world steel barrel industry in a timely manner;
2 The proportion of scientific and technical personnel in the steel drum industry has been significantly improved, and it has been able to propose a relatively perfect steel drum theory;
3 It can carry out research and development of new steel drums and new barrel equipment and materials. For example, relying on its own strength to design and manufacture high-performance barrel middle equipment, automatic, semi-automatic welding machine and spraying equipment. Can independently develop relatively advanced steel barrel sealant with good performance, etc.;
4 The technical quality of steel drum workers has been significantly improved and accumulated rich experience.
The improvement of product quality is mainly reflected in:
1 Total quality management work has been widely promoted throughout the industry;
The seven-layer arc curling technology that was not available 20 years ago has been widely used in the whole industry. The sealing reliability of steel drums has been greatly improved;
3 Domestic steel drum factory has been able to produce all kinds of demanding packaging steel drums for users;
4 steel drums look good in quality.
The improvement in the quality of steel drum industry equipment is reflected in:
1 There are more than 20 manufacturers with more advanced steel drum lines;
2 Advanced automatic welding machine, steel barrel middle section equipment, electrostatic spraying equipment, etc. have been equipped in many barrel manufacturers.
3 inspection and testing methods are improving day by day. Numerous productions. Manufacturers have been able to rely on their own strength to complete all inspection tasks from the analysis of raw materials to the finished products.
We have every reason to be proud of what we have achieved in the past 20 years, but at the same time, we should keep a clear understanding and recognize that we still have a big gap compared with our foreign counterparts. in:
1 The current situation of weak basic industries in China directly restricts the improvement of the quality of steel drums, such as the quality of steel plates, the quality of varieties and coatings;
2 The quality of the steel drum is poor. This is manifested in the fact that many manufacturers can pass various performance tests in the samples sent by the national inspection, but accidents such as leakage and leakage often occur during the user's use;
3 The appearance quality of the steel drum is still unsatisfactory. Corrosion occurs due to the appearance of the anti-corrosion layer falling off and premature failure, causing frequent occurrences of quality accidents;
4 From the perspective of the whole industry, the automation and degree of steel drum production are still not high. The phenomenon of steel barrel production using human sea tactics still exists in many enterprises.
In the past 20 years, through the introduction of technology, we have imported special steel drums and special barrel equipment, which has played a huge role in improving the technical level of China's steel barrel equipment and narrowing the gap with developed countries. However, at the same time, there is no blind introduction of China’s national conditions.
We know that due to the existence of monopoly in developed countries, foreign steel drum manufacturers are facing large-scale refineries and large-scale chemical plants, which have large and concentrated steel drums. Under this circumstance, the requirements of the barrel mills in foreign steel barrels are kiosk efficiency, high automation (reducing expensive labor costs), plus the development of basic industries, the quality of barrel materials, and all of them. To make it highly automated, the high-speed and large-volume production of the original intention can become a reality.
In China, due to the weak basic industry, steel plates for steel drums often have uneven thickness, unstable material composition and extra-thickness of corners. There are often large differences in the performance parameters of different batches of chemical raw materials such as paint, powder coating and pretreatment liquid for steel drums. In addition, with the transition of China's economy to the market economy, the users of steel drum factories are increasingly diversified, and the market structure of products is gradually moving towards small batches and varieties. This is China's national conditions in China's steel drum factories.
Many equipments in the steel drum industry were introduced without considering the above national conditions, which inevitably caused the following uncommon phenomena:
1Because the quality of the steel plate does not match the “flavor†of the welding machine, many manufacturers have to let the advanced automatic welding machine sleep, and still use the old welding machine to charge the battle;
2 Because the steel barrel factory is facing a small-volume, multi-variety market, although the introduction of high-speed assembly lines, most of these equipments are idle;
3 Most of the so-called self-developed mid-section equipment in China is a replica of similar foreign equipment. Due to the imitation level of swallowing and peeling, the manufacturing precision is low, which makes these devices have a lot of problems in operation. All of this makes many equipment manufacturers unable to return expensive introduction costs (principal and interest), and many companies have carried huge debt burdens since the date of introduction.
Twenty years of review, the purpose of the draft is to remind me that Ding earnestly sums up the experience and lessons, which is beneficial to the steel barrel industry to take less detours, develop healthily and rapidly, and raise the quality of steel drums to a new level. Let the steel barrel industry move towards the 21st century with a new look.
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